W6, Nitrogen (N) Flashcards Preview

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Flashcards in W6, Nitrogen (N) Deck (25)
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1
Q

T/F: Nitrogen is the most commonly deficient nutrient in agriculture

A

True

2
Q

What happens when too much N makes it into water?

A

Algal blooms

Eutrophication

3
Q

List some N reservoirs

A

→ Atmosphere (N₂)
→ Organic N (biology)
→ Soil

4
Q

List some forms of N that are important for management

A
→ Ammonium (NH₄⁺)
→ Ammonia (NH₃⁺)
→ Nitrite (NO₂⁻)
→ Nitrate (NO₃⁻)
→ Nitrogen dioxide (NO₂)
→ Nitric oxide (NO)
→ Nitrous oxide (N₂O)
5
Q

Explain the processes and products of denitrification

A

2NO₃⁻ (nitrate) → 2NO₂⁻ (nitrite) → 2NO (nitric oxide) → N₂O (nitrous oxide) → N₂ (nitrogen gas)

→ Nitrate replaces oxygen as the electron acceptor in soil microbial respiration
*** Denitrification occurs under anaerobic conditions
▪︎ waterlogged soils
▪︎ poorly aerated soils
▪︎ anaerobic microsites
▫︎ inside soil aggregates
▫︎ rhizosphere (root and microbial respiration)
* There will be small niches of denitrification in even the best soils.

6
Q

T/F: Volatilisation is higher in acid soils than alkaline soils.

A

False. Volatilisation is higher in ALKALINE soils.

7
Q

How does inorganic N fertilisation affect the soil?

A
↑ Plant growth
↑ Requirement for other nutrients = ↓ [nutrient]
↑ Microbial activity
↑ OM decomposition rate
↓ SOC
↓ Potentially mineralisable N
8
Q

Roughly how much of the energy consumed during crop production comes from industrial N fertiliser production?

A

30-70%

9
Q

List some ways that N fluxes in the soil

A
→ N fixation
     ▪︎ biological
     ▪︎ industrial
     ▪︎ lightning
→ Assimilation (plant uptake)
→ Immobilisation (microbial uptake)
→ Mineralisation
→ Denitrification
→ Volatilisation
10
Q

Describe the mobility of N in soil.

A

NO₃⁻ (nitrate) = very mobile due to negative charge

NH₄⁺ (ammonium) = less mobile, can be adsorbed to soil particles. Rapidly converted to NO₃⁻.

11
Q

T/F: Nitrification is an aerobic process

A

True

12
Q

T/F: Denitrification is an aerobic process

A

False.

13
Q

T/F: N concentration in soil will differ before and after rainfall

A

True.

14
Q

How is N lost from the soil, and in what proportions?

A

→ Plant uptake: 55%
→ Leaching: 16%
→ Soil erosion: 15%
→ Gaseous N losses: 14%

15
Q

How much of the world’s energy consumption is devoted to industrial N fixation?

A

≈ 1%

16
Q

What is it that makes root (N) nodules pink?

A

Leghaemoglobin

17
Q

How are plant-rhizobia symbiosis (nodules) formed?

A

→ Signalling between rhizobia and plant root
→ Rhizobia attach to plant root, root curls around rhizobia
→ Rhizobia degrade cell wall of root and cause the root plasma membrane
→ Rhizobia create infection thread which penetrates the cortex
→ Rhizobia enter cortical cell, stimulate cell division and become bacteroids (nondividing endosymbiotic organelles)
→ Bacteriod-containing cells form a nodule

18
Q

How much N can lucerne fix /ha /yr?

A

300-350

19
Q

How much N can be fixed by:
• Symbiosis (Rhizobium, Actinomycetes)
• Associations (Azospirillum, Azotobacter)
• Free-living (Azotobacter, Klebsiella)

A

→ Symbiosis: 20-400 kg N /ha /yr
→ Associations: 10-200 kg N /ha /yr
→ Free-living: 10-80 kg N /ha /yr

20
Q

If you could only know one soil property to give you an idea about that soil’s likelihood to leach nutrients, what would it be?

A

It’s texture. Sand = strong likelihood of leaching, clay = low leaching risk.

21
Q

What effect does nitrate addition and the presence or absence or mycorrhiza have on plant biomass production and nitrate leaching?

A

+ N = incr biomass, incr leaching

+ myc = incr biomass, decr leaching (by ~40x)

22
Q

T/F: N2O has a global warming potential (GWP) much greater than CO2.

A

True

23
Q

T/F: N2O production is generally lower in Australian agriculture.

A

False, it’s ≈65% higher in Aust.

24
Q

What proportion of nitrous oxide (N₂O) emissions in Australia come from agriculture?

A

≈ 80%

25
Q

How can farmers and land managers minimise N losses?

A

→ Use applied N more effectively and efficiently
▪︎ Right amount
▪︎ Right time of year
▪︎ Right method
→ Maintain soil cover (cover crops)
▪︎ Captures nutrients that would otherwise be lost
▪︎ ↓ erosion
→ Improve soil structure
▪︎ Conservation tillage
→ Increase SOM
▪︎ Adsorb more N
▪︎ ↓ runoff and erosion
→ Decrease erosion
→ Livestock (and their waste) management
▪︎ Keep livestock and their waste away from water bodies
▪︎ Maintain effluent ponds and monitor for overflow risk
→ Avoid overly alkaline conditions
→ Promote mychorriza
→ Intercept N before it is leached beyond the root zone
→ Apply management strategies that control N speciation (↓ NO₃⁻ losses by maintaining NH₄⁺)